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10 June 1999 AGE-NC Project No 97-0290 ' Page 3 of 26 of the 47 samples analyzed Petroleum hydrocarbons were not detected in soil samples ' analyzed from borings MW1, MW3, MWS, MW8 and B5 Oxygenates were not detected in the 13 samples analyzed by EPA Method 8260 Analytical results of soil samples are summarized on Tables 2 and 3 The approximate extent of Impacted soil is Illustrated on Figures 3, 4 and 5 Lines of cross section are shown on Figure 3 • The highest concentrations of petroleum hydrocarbons in soil were detected near the ' southeast portion of the site at depth intervals of 15 to 25 feet bsg and 35 to 50 feet bsg in bonngs P3,MW2 and SWI Lower concentrations of hydrocarbons were detected in borings I B4, MW4 and B6 at depths of 35 to 60 feet bsg, corresponding to historical ground water levels Impacted soil at depth appears to be concentrated in a silt and clay interval between approximately 40 to 47 feet bsg (Figures 4 and 5) • The permeability of samples 134-25, MWi-30 and MW3-55 was measured at 2 2 x 10', 3 5 x 10 3 and 3 3 x 10 ', respectively Porosity ranged from 32 26 percent to 41 16 percent Specific gravity ranged from 2 68 to 2 71 Percent organics ranged from 0 6 to 1 5 Sample 134-25 was a fine sandy silt, sample MW1-30 was a poorly-graded, medium-grained sand, sample MW3-55 was a silty fine sand Results of physical analyses are summarized on Table 4 • Highly permeable soils encountered beneath the site could potentially promote vertical migration of contaminants in the vadose zone and lateral migration of contaminants in ground water • A hard silt/clay Iayer appears to underlay the site at a depth of approximately 60 feet bsg -- This layer may act as a horizontal barrier to deeper migration of contaminants at the site Thickness of the silt/clay unit has not been determined • Historical depth to ground water at the site has ranged from approximately 35 feet bsg in 1971 to 55 feet bsg in 1993 and 1996, based upon ground water maps prepared by the San Joaquin County Flood Control and Water Conservation District between 1971 and 1996 Ground water currently occurs at a depth of approximately 43 feet bsg • Current ground water flow at the site is toward the south Historical flow may have varied due the influence of pumping of municipal wells near the site Historic operation of nearby municipal wells may account for the deeper northerly and easterly extent of contaminants from the site • TPH-g was detected at concentrations as high as 45,000 parts per billion (ppb, reported as micrograms per liter, MW-2) TPH-d was detected at concentrations as high as 4,900 ppb W H BTEX compounds were detected at concentrations as high as 5,000 ppb, 5,400 ppb, 1,200 ppb and 5,700 ppb, respectively (MW-2) • • D1PE and tertiary butanol (TBA) have been detected in water samples collected at the site Advanced GcoEnvtronmental,Inc